Walleye (Sander Vitreus) Spawning Habitat Selection and Dynamics in a North-Temperate Wisconsin Lake
File(s)
Date
2006-12Author
Raabe, Joshua K.
Publisher
University of Wisconsin-Stevens Point, College of Natural Resources
Metadata
Show full item recordAbstract
Critical to the conservation and management of sustainable populations of walleye,
Sander vitreus, throughout North America is the need to understand what comprises and
compromises high quality spawning habitat. In particular, questions remain regarding the
actual selection of spawning habitat by walleye, how physical characteristics and
functional dynamics (e.g., thermal conditions, wave energy, water levels) impact habitat
quality, and the quantity of spawning habitat necessary to sustain healthy walleye
populations. Therefore, the spawning habits and habitat of naturally reproducing walleye
in Big Crooked Lake, a north temperate Wisconsin lake, were evaluated in 2004 and
2005, with specific objectives to: 1) describe the physical characteristics of natural
walleye spawning reefs in order to develop detailed blueprints of successful natural
walleye spawning habitat and to develop walleye spawning habitat resource selection
functions, 2) evaluate thermal conditions on walleye spawning reefs and the relative
affect they have on reproductive success across two years, and 3) assess the potential
impact of wind activity, wave energy, and water level on walleye egg movement and
survival. Walleye spawned primarily close to shore (outer boundary x distance = 2.72
m), in shallow water (outer boundary x depth = 0.29 m) and over gravel substrate
( x coverage = 64.3%) with low embeddedness ( x = 1.30) at all sites. Only 39% of
available rock shoreline (14% of total shoreline) and no offshore reefs were utilized by
walleye. The best resource selection function (overall correct classification = 97.6%)
predicted that the relative probability of egg deposition increased with gravel and cobble
substrates and decreased with distance from the shoreline, higher substrate
embeddedness, and with increasing sand and fine organic material. Evaluating habitat
quality (i.e., egg survival), regression models found percent cobble substrate to be the
only variable positively related to the percent survival of deposited eggs in egg collection
chambers. Two- and three-dimensional spawning reef blueprints were developed to
visually depict the successful natural walleye spawning habitat studied. Evaluating
thermal conditions, despite gradual and stable rises in water temperature and high
densities of eggs in 2004, percent survival was lower than in 2005, potentially due to
lower thermal lethal limits (<6°C) exceeded the first six days of the spawning period. In
2005, water temperature fluctuated, prolonging the development and hatching of walleye
embryos but had minimal direct impact on egg survival. Significant differences (p <
0.05) in mean daily water temperature throughout the spawning period were observed
between reefs and sometimes within reefs. Close to shore, shallow water responded more
to fluctuations in air temperatures than further, deeper water at all reefs. Wind and wave
velocities showed a positive, significant (p < 0.001) correlation. Periods of wave energy
were sufficient to initiate movement of walleye eggs over 28% of the incubation period
and also to move various substrate size classes, potentially impacting egg survival
through transportation or exposure, abrasion, and burial. Egg movement was primarily
closer towards shore and along shorelines of the littoral zone having sand substrates.
Larger substrates and steeper riparian shoreline areas at reefs retained eggs better than
flatter sand regions. Water level fluctuations were minimal (+1.20 cm) and most likely
did not impact the amount of available habitat or strand and desiccate eggs. This study
increases our quantitative understanding of walleye spawning areas and can assist
biologists in understanding future processes affecting habitat quality and in developing
protection strategies of natural reefs and potentially aid in the design of artificial reefs.